Remember that ad-hoc conferencing and Meet Me conferencing are very different animals, although both use resources.
A single user in a Meet Me conference consumes 2 IP resources, one for the user and one for the MOH source they get connected to when only single user is connected, as more users connect the MOH resource is dropped, so 1 user in a Meet Me Conference consumes 2 "resources", 2 consumes 2, 3 consumes 3, etc. up to 20 in a single conference, and a total of 40 conference resources (on 6.0 or higher software, previous versions have less resources)